In general, in the case of dies including, for example, forging dies, press working dies, and casting dies, stress acts on a portion where the die members make mutual abutment, and on portions thereof where molten metal tends to collide at high speed. As a result, cracks and/or abrasions may occur.
The damaged portion, which appears as a crack or an abrasion on the die, brings about factors causing burrs and/or strain. Burr-removal and shaping operations, which are performed on the product during downstream steps, are consequently increased. In view of the above, in order to avoid the occurrence of defects in the product, as described above, the die is reinforced beforehand in some cases, or the damaged die may be repaired in other cases.
A conventional method is known for reinforcing a die, in which padding is performed utilizing an electric discharge coating, for portions of the die which tend to suffer from damage. In the case of such a padding method, the electric discharge coating treatment is produced as follows. That is, a high temperature caused by spark discharge is utilized so that an electrode material, which includes, for example, metal, ceramic carbide, and cermet, is vapor-deposited onto the surface of portions of the die suffering from damage, to perform surface treatment for improving, for example, hardness, corrosion resistance, and durability (see, for example, Japanese Laid-Open Patent Publication No. 01-210133).
The reinforcing method described above may also be applied in relation to repairs performed when damaged portions appear on the die as well.
However, in the reinforcing and repair methods described above, the joining strength is weak and brittle at the joined area between the padding portion and the die, and therefore durability thereof is limited. Thus, there is a drawback in that the reinforcement or repair must be performed frequently, resulting in a consequent lowering of productivity.
In particular, in the case of a forging die, the padding portion tends to become exfoliated due to high stress exerted during use, in addition to thermal fatigue. In this case, it is difficult to perform reinforcement and repair by means of such padding. Therefore, when the forging die becomes damaged, the forging die must be scrapped, resulting in economic loss.